Data from: Brain size in birds is related to traffic accidents

Estimates suggest that perhaps a quarter of a billion birds are killed by traffic annually across the world. This is surprising because birds have been shown to learn speed limits. Birds have also been shown to adopt to the direction of traffic and lane use, and this apparently in reduced risks of mortal traffic accidents. Such behavioral differences suggest that individual birds that are not killed in traffic should have larger brains for their body size. We analyzed the link between being killed by traffic and relative brain mass in 3521 birds belonging to 251 species brought to a taxidermist. Birds that were killed in traffic indeed had relatively smaller brains, while there was no similar difference for liver mass, heart mass or lung mass. These findings suggest that birds learn the behavior of car drivers and hunters, and that they use their brains to adjust behavior in an attempt to avoid mortality caused by rapidly and predictably moving objects.